One greatly regretted that it was necessary to mark the reply according to its ignorance, and not, as one would have wished, in proportion to its ingenuity. Magnetic declination, however, as everybody knows, measures the deviation of the 'needle' from the true geographical north and south direction; the inclination or dip is the angle which a 'needle' makes with the horizon. At one time the only method of watching the movements of the magnetic needles was by direct observation, just precisely as it was wont to be in the case of the barometer and thermometer. But the same agent that has been called in to help in their case has enabled the magnets also to give us a direct and continuous record of their movements. In principle the arrangement is as follows: A small light mirror is attached to the magnetic needle, and a beam of light is arranged to fall upon the mirror, and is reflected away from it to a drum covered with sensitive paper. If, then, the needle is perfectly at rest, a spot of light falls on the drum and blackens the paper at one particular point. The drum is made to revolve by clockwork once in twenty-four hours, and the black dot is therefore lengthened out into a straight line encircling the drum. If, however, the needle moves, then the spot of light travels up or down, as the case may be. Now, if we look at one of these sheets of photographic paper after it has been taken from the drum, we shall see that the north pole of the magnet has moved a little, a very little, towards the west in the early part of the day, say from sunrise to 2 p.m., and has swung backwards from that hour till about 10 p.m., remaining fairly quiet during the night. The extent of this daily swing is but small, but it is greater in summer than in winter, and it varies also from year to year. [Illustration: MAGNETIC PAVILION--INTERIOR. (_From a photograph by Mr. Lacey._)] Besides this daily swing, there occasionally happen what are called 'magnetic storms;' great convulsive twitchings of the needle, as if some unseen operator were endeavouring, whilst in a state of intense excitement, to telegraph a message of vast importance, so rapid and so sharp are the movements of the needle to and fro. These great storms are felt, so far as we know, simultaneously over the whole earth, and the more characteristic begin with a single sharp twitch of the needle towards the east.